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The atexit module defines functions to register and unregister cleanup
functions. Functions thus registered are automatically executed upon normal
interpreter termination. atexit runs these functions in the reverse
order in which they were registered; if you register A, B, and C,
at interpreter termination time they will be run in the order C, B,
A.

Note: The functions registered via this module are not called when the
program is killed by a signal not handled by Python, when a Python fatal
internal error is detected, or when os._exit() is called.

Changed in version 3.7: When used with C-API subinterpreters, registered functions
are local to the interpreter they were registered in.

Register func as a function to be executed at termination. Any optional
arguments that are to be passed to func must be passed as arguments to
register(). It is possible to register the same function and arguments
more than once.

At normal program termination (for instance, if sys.exit() is called or
the main module’s execution completes), all functions registered are called in
last in, first out order. The assumption is that lower level modules will
normally be imported before higher level modules and thus must be cleaned up
later.

If an exception is raised during execution of the exit handlers, a traceback is
printed (unless SystemExit is raised) and the exception information is
saved. After all exit handlers have had a chance to run the last exception to
be raised is re-raised.

This function returns func, which makes it possible to use it as a
decorator.

Remove func from the list of functions to be run at interpreter
shutdown. After calling unregister(), func is guaranteed not to be
called when the interpreter shuts down, even if it was registered more than
once. unregister() silently does nothing if func was not previously
registered.

The following simple example demonstrates how a module can initialize a counter
from a file when it is imported and save the counter’s updated value
automatically when the program terminates without relying on the application
making an explicit call into this module at termination.